1. Field of the Invention
This invention relates to methods of production, and more particularly, to methods for producing a plurality of similar plastic parts by injection molding and thereafter providing different readable indicia on or within the plastic parts.
2. Prior Art
In a prior U.S. patent application, Ser. No. 179,040, allowed June 18, 1981, now U.S. Pat. No. 4,307,047 the teachings of which are incorporated herein by reference, a method of manufacture of identical parts displaying different indicia is disclosed. In that method, the parts are injection molded out of a base material plastic to which a filler has been added. The plastic in the base material of the part is mixed with a filler which is capable of being changed in color by means of applied energy radiation. Subsequent to mixture of the plastic-filler mixture, the uniform parts are injection molded through the use of a uniform tool such that identically shaped parts are provided. Thereafter, the standard parts are subjected to an energy radiation which is accomodated to the shape of the symbol which is to be applied thereby correspondingly changing the color of the surface of the part at the location of impact by the energy radiation.
In the prior disclosed method, a preferred base plastic was ABS whereas the filler was a color powder which responded to thermal radiation such as, for example, that available from Farber Castell under the trademark "Thermocolor". The applied energy radiation was preferably by means of deflectable laser played over the surface of the part.
In this manner, plastic keys could be manufactured whose indicia was a fixed part of the base material as opposed to an applied part common with printed keys. Thus, the product, although initially identically produced in volume, was, after creation of the readable indicia, substantially corresponding to the quality standard previously had in two-color injection molded plastic keys.